This invention relates to a drive unit, a drilling rig for subsoil drilling, and to a method of handling tube sections using such equipment. Handling of tube sections occurs, for example, in the course of placing and removing a casing in a bore hole in the lithosphere and in the course of drilling a bore hole and tripping (removing and/or reintroducing a string of joints into a bore hole).
Conventionally, handling of, for instance, casing sections in a rotary well drilling rig is carried out in the following manner. Starting from a situation in which a string of casing is suspended from a spider at the rig floor and extends downwards in a bore hole, a protecting and guiding device is mounted to the connector forming the top end of the casing string suspended from the spider. Then a next casing section is attached to a joint elevator, which is cable mounted to a drive unit, and hoisted into a vertical orientation freely suspended above the floor of the well head as the block carrying the drive unit is lifted. During lifting, the casing section is guided to prevent damage of the external, unprotected thread at its bottom end. A stabbing board is moved toward the tube string elevator mounted to the drive unit.
Subsequently, the block is slowly moved down and the thread at the bottom end of the section to be attached is guided by a roustabout into the casing connector at the top end of the string suspended from the bottom spider elevator. Then the protecting and guiding device is removed and the block moves down further until the casing section to be attached stands on thread on the string to which it is to be attached. Then a casing tong is moved into an operating position and the casing section is moved to and fro at its top end and rotated until the thread at its lower end and the thread at the top end of the casing string is projecting from the bore hole mate. This involves close cooperation of the person orienting the casing to be attached (the stabber) and the person operating the casing tong (also known as Weatherford tong).
After the connection between the casing section and the casing string has been made, the block moves down and the stabber guides the top end of the casing into the tube string elevator. Then the joint elevator is disengaged and the stabbing board is moved back into its parking position. Then the casing tongs are activated and the casing is rotated until the threads fully mate and the required make-up torque is reached. The casing tong is then moved back to its parking position.
If the casing string needs to be washed down, the block is lowered somewhat further, so that the top end of the newly attached case joint is introduced into a sealing for providing a sealed high pressure mud supply to the casing string (an example of such a coupling apparatus is described in international patent application WO 92/11486). Then the newly attached casing section is filled with mud or, if the casing needs to be washed down, mud at a pressure of up to about 60 bar is circulated down the casing to wash down the casing.
To lower the casing string with the newly attached casing section into the bore hole, the casing string is briefly lifted, which allows the spider to disengage, and the block carrying the drive unit from which the string is suspended is lowered to just above the floor. Finally, the spider engages the string again and the block is lowered a little more to allow the tube string elevator to disengage. Then the above cycle is repeated until the entire casing string in the well is completed.
The connection and disconnection between drill pipe sections and a drill pipe string in a bore hole involves a slightly different method of making up and breaking the connections and of suspending the string from the drive unit. However, irrespective of the type of tube sections which are connected or disconnected, these methods are cumbersome, time-consuming and laborious. A very important disadvantage of the laborious nature of these methods is that many persons have to be present in an area where there is a high risk of accidents in terms of falling objects, explosions and the like. Other problems include limited visibility of the upper end of a casing section as it is introduced in the tube string elevator.
In U.S. Pat. No. 3,766,991 a drive unit according to the introductory portion of claim 1 and a method according to the introductory portion of claim 13 are described. In the particular drive unit as described, the device for engaging the tube sections and the drive connected thereto are tiltable to allow the introduction of tube sections into the engaging unit from the side. This, however, entails the disadvantage of a complex and expensive construction of the drive unit, in particular if tube sections of sizes typically used as drill or casing tubes of an oil or gas well are to be handled, and requires a precise positioning of the tube section to be introduced from the side relative to the engagement unit of the drive unit which is suspended by cables, and a close coordination of the feeding of tube sections and the vertical movement of the drive unit. Such methods are inherently time-consuming, which has a negative effect on the productivity of a rig.
It is an object of the present invention to make handling of tube sections in a rig for subsoil drilling safer and more efficient without entailing the disadvantage of a complex and expensive construction of the drive unit.
According to the present invention, this object is achieved by providing a drive unit according to claim 1. Other embodiments of the invention are formed by a rig for subsoil drilling according to claim 10 and a method for handling tube sections in a rig for subsoil drilling according to claim 13.
By providing the drive unit with a gripper which is movable relative to the engagement unit of the drive unit between a first position for gripping a tube extending along the tube string axis and engaged by the engagement unit, and a second position for gripping a tube radially directed towards the tube string axis, supplied tube sections can be gripped and movements of supplied tube sections relative to the engagement unit in the drive unit can be guided and controlled accurately until the tube sections are engaged by the engagement unit. It is not necessary to tilt the engagement unit, and co-ordination of positions and movements between the supplied tube sections and the drive unit is simplified.
Particularly advantageous embodiments are described in the dependent claims. Further objects, embodiments and details of the present invention are set forth in the description below and the accompanying drawings.